1. Field of the Invention
The present invention relates to an inkjet recording apparatus that performs recording using a recording head for ejecting ink, and a method for controlling it.
2. Description of the Related Art
When nozzles of an inkjet recording apparatus have not ejected ink for a long time, water evaporates not only from the mouths of the nozzles but also from liquid chambers at the backs of the nozzles, and thickened ink occupies the insides of the nozzles. If an image is recorded in this state, the thickened ink may cause an image defect. In order to prevent ejection defects of nozzles or thickening of ink due to water evaporation from nozzles, preliminary ejection is performed. For example, in an apparatus that uses a line head as a recording head and performs prolonged continuous recording on roll paper, preliminary ejection is performed onto a recording medium (roll paper) between image recording operations.
Japanese Patent Laid-Open No. 11-10908 discloses a technique in which ink is circulated along an ink passage in a recording head and the amount of ink to be circulated is varied according to the temperature of the recording head. By circulating ink, a constant ink temperature in the recording head can be maintained, and thickened ink in the liquid chambers at the backs of the nozzles is diffused.
However, even if ink is circulated in the recording head, preliminary ejection is necessary to prevent image defects due to thickening of ink. At each bend of the ink circulation passage, the outer side of the bend is inefficient in diffusion and movement of ink compared to the middle of the bend. Therefore, during preliminary ejection, thickened ink tends to remain on the outer side of the bend.